Many enclosures that contain sensitive instrumentation must maintain very clean environments in order for the equipment to operate properly. Examples include enclosures with sensitive optical surfaces or electronic connections that are sensitive to particles and gaseous contaminants which can interfere with mechanical, optical, or electrical operation, data recording devices such as computer hard disk drives, enclosures for processing, transporting or storing thin films and semiconductor wafers, electronic control boxes such as those used in automobiles and industrial applications. Contamination in such enclosures originates from both inside and outside the enclosures. For example, in computer hard drives, damage may result from external contaminants as well as from particles generated from internal sources. The terms “protective enclosures” will be used herein for convenience and are understood to include any of the enclosures mentioned above.
To address particulate contamination, internal particulate filters, or recirculation filters, may be installed in protective enclosures. These filters typically comprise an inner layer of electret media disposed between two or more outer scrim layers. Electret media is generally comprised of fibrous media. The fibers may be charged to improve the removal efficiency of the media. However, the fibers of the electret may present problems. The fibers may separate from the filter or project from the surface. This may cause damage to sensitive components within an enclosure.
Scrim layers may be useful to contain fibers, increase stiffness and improve filter handling. Known scrim layers include non-wovens, wovens, spun-bonds, knits, net like polymeric materials. Scrim layers may also be a source of fiber problems, as the scrim materials can themselves generate protruding fibers. Moreover, these known scrim materials may provide stiffness and some level of fiber containment, there still exists a need for a recirculation filter with a scrim layer capable of improved fiber containment without compromising its particle filtration performance within the drive. The improved recirculation filter of the present invention meets such a need.